innovations conference 2014 prof peter metcalfe moving towards mri along radiation therapy...
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Professor Peter Metcalfe - Moving Towards MRI Alone Radiation Therapy Treatment Planning: What is the Impact of MRI DistortionTRANSCRIPT
Peter Metcalfe*, Amy Walker, Gary Liney, Lois Holloway
Centre for Medical Radiation Physics, University of WollongongLiverpool and Macarthur Cancer Therapy Centres and Ingham Institute
Moving towards MRI alone radiation therapy
treatment planning:
What is the impact of MRI distortion?
* Acknowledge support from Cancer Institute NSW Clinical Leaders Program
1. Current MRI/CT in Radiotherapy Planning (RTP)
2. Challenges to MRI alone RTP
3. Quantifying MRI distortion
4. Impact of MRI distortion on RTP
5. Current X-ray Image Guided Radiation Therapy
6. MRI for Image Guided Radiation Therapy?
Content
CT
CT MR
MRI
1. Current MRI/CT in RTP
MRI better soft tissue contrast
Process - CT scan + MRI scan
Register MR contours to CT (rigid/deformable)
Transfer MR contours onto CT data set
CT MR
1. Current MRI/CT in RTP
Courtesy Google Images
Why do we plan using CT data?
CT number to electron density
Geometric certainty of CT
Technology in Cancer Research & Treatment 2013 April 24. Epub ahead of print
MRI in Radiation-therapy Treatment Planning 5
Site-specific Use of MRI in Radiotherapy
Treatment Planning
This section reviews clinical trials of sites for which vari-
ous MRI sequences and analysis methods have been useful
in cancer management. The sites selected for review cover
brain, head and neck, breast, lung, prostate and cervix, and
are not intended to be exhaustive.
Brain
Owing to its small size and central location within the mag-
net, the brain is one of the easiest organs to image well.
MRI is well established as the superior imaging modality
for diagnostic purposes when assessing the brain. In the
brain, MRI often provides better visualization of tumor
and normal tissue than CT, and hence the target volume for
high-precision intracranial radiotherapy is commonly delin-
eated directly on MRI studies (Figure 2). It can be imaged
in standard diagnostic RF coils usually in the treatment
position, and its registration to CT is trivial even with dif-
ferences in position.
The brain was the first site where MRI was routinely used
in treatment planning. Routine clinical use of MRI in the
treatment-planning process of fractionated radiotherapy (RT),
Figure 2: CT (left) co-registered with a T1-3D-SPGR MRI image set (right). The difference in tumor visualization can be clearly appreciated.
Figure 1: 3He polarization image showing polarized MR helium 3 diffusion scan (right) fused on a proton-density-weighted MR scan (left). These active
zones would be the regions of conformal avoidance, defined as low-dose objectives during the radiotherapy treatment planning process.
CT MR
2. Challenges to MRI alone RTP
B field inhomogeneity
Non linear gradients
from RF excitation
Displacement of signal
from actual location
Apparent signal
location
Real signal location
3. Quantifying MRI distortion
Sunrise Phantom
Poly-ethylene
+5830 Vitamin E Capsules
length 513 mm
diameter 500 mm
height 350mm
Amy Walker
PhD student
3. Quantifying MRI distortion
MRI moving couch MRI static couch
3. Quantifying MRI distortion
Moving couch MRI Static couch MRI
Centre
Slice
Extreme
slice # 2
(~216 mm
from
phantom
centre)
S
Experimental Method:
Measure MRI distortion on phantom
Apply distortion map to CT on
patient images
RTP plan on ‘distorted’ CT dataset
Plan copied onto ‘undistorted” CT
Assess dosimetric impact (e.g. DVH)
4. Impact of MRI distortion on RTP
* CTV Breast
* Cont. Breast
* Lungs
* Heart
Superior
Inferior mm
MILXView
Coronal
Acknowledge Jason Dowling CSIRO
4. Impact of MRI distortion on RTP
http://aehrc.com/research/biomedical-imaging/software-solutions/milxview
Dosimetric variations:
15 breast tangent IMRT treatment plans
Plans optimised on distorted data met dose
criteria when reviewed on original CT
Less than 3% variation in PTV coverage
OAR dose variations low
4. Impact of MRI distortion on RTP
Literature
Metcalfe P, Liney G, Holloway L, Walker A, Barton M, Delaney G,
Vinod S, Tome W (2013)
”The potential for an enhanced role
for MRI in radiation-therapy treatment planning”
Technology in Cancer Research and Treatment
Review Article
12(5) 429-446
Speculative
Walker A, Liney G, Metcalfe P,
Holloway L (2014)
"MRI distortion: considerations for
MRI based radiotherapy
treatment planning”
Australasian Physical &
Engineering Sciences in
Medicine.
37 (1), 103-113.
Philips 1.5 T 60 cm bore scanner-T2 turbo spin echo
AAPM 2D phantom
Literature
Fiducial markers
Surrogate for soft-tissue
alignment
Then make couch shift
Courtesy: http://c431376.r76.cf2.
rackcdn.com/37184/fonc-02-00172-HTML
/image_m/fonc-02-00172-g003.jpg
Gold Marker and needle
Reference Wikipedia images
5. Current X-ray Image Guided Radiation
Therapy?
17
Australian MRI-Linac Program
U Alberta- Rotating Magnet
Viewray-MRIdian MRI-Cobalt
U Utrecht-Philips Elekta
http://www.viewray.com
6. MRI for Image Guided Radiation Therapy?
MR-IGRT
Prototype at Liverpool Hospital - Ingham (Sydney)
CT MR
http://inghaminstitute.org/Mri-linac.html
NHMRC Grant Principal Investigators: Paul Keall, Michael Barton and Stuart Crozier
6. MRI for Image Guided Radiation Therapy?
Orientation Questions?
Inline
Electron Focus Effect
(EFE)
Transverse
Electron Return Effect
(ERE)
6. MRI for Image Guided Radiation Therapy?
Dosimetry Questions?
MP512 – Diode Array – 2mm pitchCourtesy Maegan Gargett
PhD student CMRP
6. MRI for Image Guided Radiation Therapy?
3T MRI of MP512
Rapid MR Imaging
Real-time Position
Estimation
Slide adapted from images
courtesy of Paul Keall, U Sydney
6. MRI for Image Guided Radiation Therapy?
Goal
Real-time adaptive radiation therapy
Accounting for anatomic soft tissue
Questions?
Peter Metcalfe email: [email protected]
http://inghaminstitute.org/Mri-linac.htmlSiemens 3T MRI at Liverpool Cancer Care, Sydney